1. Field of the Invention
The present invention is directed to a method and system for generating a sequence of structured light patterns for use in illuminating a three-dimensional object in preparation for 3-D digital data capture and object rendering.
2. Background
U.S. Pat. No. 6,512,844 to Bouguet et al., entitled “3D Rendering”, discloses a technique for capturing the surface of three-dimensional (“3D”) objects using structured lighting. The movement of a shadow, formed by a wand, stick or other pencil-like object, across a 3D object is optically recorded. Variation in brightness on the surface provides a cue for triangulation. By analyzing the variation in brightness of a particular point on the surface, the location of that point is determined based on the movement of the shadow. With known locations for a camera and a light source, the coordinates in space of the point is triangulated. By repeating this process, a collection of coordinates is created. Those coordinates are then used to reconstruct the 3D surface.
U.S. Pat. No. 6,549,288 to Migdal, et al., entitled “Structured-light, Triangulation-Based Three-Dimensional Digitizer”, is directed to a system for illuminating an object with a special kind of structured light pattern, recording the shape of the reflected points of light by means of a camera, and reconstructing the 3D shape of the object through a computer using the data points collected from the reflection of the structured light pattern. The reconstruction is performed using a triangulation technique that does not depend on the fixed direction of the light source relative to the camera. The system stores several images of the objects with different illumination patterns. The data is subsequently processed, by a computer system which applies data processing routines, i.e., the model building algorithms which provide 3D surface generation. The data acquisition is simplified to acquiring of only two or, optionally, four images of the object, thereby significantly increasing the digitization speed over that of laser-based scanners. The light source projects both structured light and uniform illumination light from the same apparent source, and that allows for numerical normalization of the images.
U.S. Pat. No. 7,103,212 to Hager et al., entitled “Acquisition of Three-dimensional Images by an Active Stereo Technique Using Locally Unique Patterns” discloses a system and method for acquiring three-dimensional (3-D) images of a scene. The system includes a projection device for projecting a locally unique pattern (LUP) onto a scene, and sensors for imaging the scene containing the LUP at two or more viewpoints (i.e., at two or more cameras). A computing device matches corresponding pixels in the images by using the local uniqueness of the pattern to produce a disparity map. A range map can then be generated by triangulating points in the imaged scene.
U.S. Pat. No. 7,146,036 to An Chang et al., entitled “Multiframe Correspondence Estimation”, is directed to systems and methods of multiframe correspondence estimation. Light patterns reflected from the scene are captured at one or more capture planes (i.e., at one or more cameras). In one aspect, a sequence of patterns of light symbols that temporally encode two-dimensional position information in a projection plane with unique light symbol sequence codes is projected onto a scene. A correspondence mapping between multipixel regions in the capture plane and corresponding regions in the projection plane is computed based at least in part on correspondence between light symbol sequence codes captured at the capture plane and light symbol sequence codes projected from the projection plane. In another aspect, the patterns consist of a single plane of light that is swept across the scene. Correspondence is determined based at least in part on exploiting the epipolar constraint associated with any pair of cameras.
U.S. Published Patent Application No. 2005/0088259 to Geng, entitled “System and Method For Three-Dimensional Imaging Systems, discloses an approach for acquiring a surface profile 3D data set of an object. The approach includes illuminating a surface of the object with a sequence of multiple rainbow projection (MRP) structural light patterns, capturing light reflected from the object, and calculating 3D data (X, Y, Z) for each visible point on the object based upon triangulation mathematical principles of the captured reflected light.
U.S. Published Patent Application No. 2007/0115484 to Huang et al., entitled “3D Shape Measurement System and Method Including Fast Three-Step Phase Shifting, Error Compensation and Calibration”, discloses a structured light system for object ranging/measurement. The disclosed system implements a trapezoidal-based phase-shifting function with intensity ratio modeling using sinusoidal intensity-varied fringe patterns to accommodate for defocus error. The structured light system includes a light projector constructed to project at least three sinusoidal intensity-varied fringe patterns onto an object that are each phase shifted with respect to the others, a camera for capturing the at least three intensity-varied phase-shifted fringe patterns as they are reflected from the object and a system processor in electrical communication with the light projector and camera for generating the at least three fringe patterns, shifting the patterns in phase and providing the patterns to the projector, wherein the projector projects the at least three phase-shifted fringe patterns sequentially, wherein the camera captures the patterns as reflected from the object and wherein the system processor processes the captured patterns to generate object coordinates.
One problem with using waveforms having a sinusoidal intensity is to illuminate an object for 3-D rendering, such as disclosed in U.S. patent application no. 2007/0115484, is that ambiguities may arise during image matching. These ambiguities are the result of the very small differences in intensity from one pixel to the next, near the peaks and troughs of the waveform.